In general, additives are used in a copper electroplating solution. Additives include a promoter and a retardant, and when added to a plating solution, then the plating on the bottom of a via-hole is promoted while that outside the via-hole is retarded whereby the via-hole is filled with a plating metal. To attain the phenomenon, the promoter and the retardant used must be well balanced in point of their effects, and the concentration control of the additive components is important.
One method proposed for the concentration control of additives is CV (cyclicvoltammetry) (e.g., see R. Haak, C. Ogdan, D. Trench: Plating 64 (4), April 1981). The basis of CV analysis is that, when a voltage is imparted to the inactive electrode in a plating solution and the potential is linearly scanned, then the additive in the solution changes the polarization for copper deposition reaction thereby having an influence on the amount of the deposited copper. The amount of the deposited copper plating thus measured is in proportion to the quantity of electricity having passed through the inactive electrode, and therefore, when the quantity of electricity is measured, then the effect of the additive to change the polarization may be evaluated.
A method that employs this conception is CVS (cyclic voltammetry stripping). Periodically changing the potential applied to an electrode, copper plating on the surface of the electrode and stripping from it is repeated, and the quantity of electricity for stripping is measured as a criterion for the amount of the plating copper. From the ratio of the plating amount with a solution having a known concentration and that with the in-field solution to be analyzed, the additive concentration in the in-field solution is computed.
In spite of the assertion, that CV is usable as an additive control apparatus and of the effectiveness of commercially-available CVS apparatus, there are posed many technical problems. For example, in copper electroplating for filling vias, there is a problem in that the fillability with the plating solution is worsen with the lapse of time after the preparation of the plating bath, even though the additive concentration in the solution is controlled through CVS analysis. This will be because, though the additive component decomposes during plating and therefore its effect reduces, even the component having such a reduced effect may be detected as the additive concentration in CVS analysis.